title: Gigantism in unique biogenic magnetite at the Paleocene-Eocene Thermal Maximum.
abstract: We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene-Eocene Thermal Maximum (PETM) in a borehole at Ancora, NJ. Aside from previously described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 microm long and hexaoctahedral prisms up to 1.4 microm long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin. Electron holography indicates single-domain magnetization despite their large crystal size. We suggest that the development of a thick suboxic zone with high iron bioavailability--a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming--drove diversification of magnetite-forming organisms, likely including eukaryotes.
authors.affiliation: Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montréal, QC, Canada H3A 2A7.
authors.forename: Dirk
authors.initials: D
authors.lastname: Schumann
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Raub
authors.forename: Robert E
authors.initials: RE
authors.lastname: Kopp
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Guerquin-Kern
authors.forename: Ting-Di
authors.initials: TD
authors.lastname: Wu
authors.forename: Isabelle
authors.initials: I
authors.lastname: Rouiller
authors.forename: Aleksey V
authors.initials: AV
authors.lastname: Smirnov
authors.forename: S Kelly
authors.initials: SK
authors.lastname: Sears
authors.forename: Uwe
authors.initials: U
authors.lastname: Lücken
authors.forename: Sonia M
authors.initials: SM
authors.lastname: Tikoo
authors.forename: Reinhard
authors.initials: R
authors.lastname: Hesse
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Kirschvink
authors.forename: Hojatollah
authors.initials: H
authors.lastname: Vali
mesh_terms: D000538:Aluminum Silicates / Q000032:analysis; D000077215:Clay; D004777:Environment; D052203:Ferrosoferric Oxide / Q000737:chemistry* / Q000378:metabolism; D019015:Geologic Sediments / Q000737:chemistry* / Q000382:microbiology; D049690:History, Ancient; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D010103:Oxygen Isotopes; D013997:Time Factors
chemical_list: D000538:Aluminum Silicates; D010103:Oxygen Isotopes; D000077215:Clay; D052203:Ferrosoferric Oxide